U.S. Pat. No. 3,922,239 describes a mixture of cellulose esters or ethers which are mixed with polymeric cyclic esters, such as for example the oligomer of .epsilon.-caprolactone. This substance is said to be thermoplastic. It was found that the components of the mixture do not posses satisfactory compatibility. This is shown by the fact that during the thermoplastic processing no homogeneous melt is obtained. To some extent even a de-mixing can be observed during the processing.
GR-A-2 152 944 describes plasticized cellulose acetates. These are obtained in the reaction of a cellulose acetate having a free hydroxyl group, with a cyclic ester, in particular in the form of .epsilon.-caprolactone, in the presence of a catalyst. The ratio of weights of the cellulose acetate to the cyclic ester is said to be between 1/99 and 95/5 and the polymerization temperatures are said to be between 120.degree. and 230.degree. C. The reaction is preferably carried out in dry nitrogen as a protective gas. The reaction mixture can comprise an organic solvent containing no active hydrogen in the molecule and showing sufficient compatibility with the cellulose acetate and the cyclic ester, such as for example xylene. Possible catalysts are in particular organic acids, inorganic acids, alkali metals, such as sodium and potassium, tertiary amines, alkyl aluminum and its derivatives, such as triethyl aluminum, alkoxy titanium compounds, such as tetrabutyl titanate, organometallic compounds such as stannous octoate and dibutyl tin dilaurate, and metal halogenides, such as tin chloride. The quantity of cyclic ester which is to be reacted with the hydroxyl group-containing cellulose acetate, is preferably between 0.5 and 4.0 mol units per anhydroglucose unit of the cellulose acetate. The melting temperature of the plasticized cellulose acetate is reduced through an "inner" plastification. The decomposition temperature is simultaneously raised. This permits the plasticized cellulose acetate to be spun into filaments in advantageous manner in the melt. These are used inter alia in the field of textiles and for the production of cigarette filter tows.
The process and the plasticized cellulose acetates described in GB-A-2 152 944 are in need of improvement. The use of caprolactone-grafted cellulose acetate, corresponding to the component A without component B (as will be described in the following) requires a high content of caprolactone in order to ensure processing out of the melt. This is relatively expensive. Moreover, it would be desirable to lower the melting point of the plasticized cellulose acetate even further in order to utilize to an increased degree the advantages of spinning from the melt compared to dry spinning. The dry spinning process is afflicted with the disadvantages that the solvents used must be recovered which is economically as well as ecologically disadvantageous.
Prior art, as published in the following publications, does not go beyond that of the above discussed GB-A-2 152 944: WO 92/20738 describes degradable cellulose esters comprising a hydrophilic degradation activator. Under high ambient moisture this diffuses into the cellulose ester and makes it degradable. The degradation activator can inter alia be a lactone. It can also be considered as a plasticizing agent for the cellulose ester. Conventional plasticizing agents can additionally be used. U.S. Pat. No. 4,529,788 deals with a process for the production of graft polymerizate in which a cyclic ester is subjected to a catalyzed ring-splitting polymerization in the presence of a cellulose derivative. The graft polymerizate has high transparency, good film-forming properties and high solubility. Derwent Abstract 86-242456/37 of J 61171719 relates to polyurethanes of improved miscibility with other polymerizates with organic diisocyanates being converted with polyester polyols, which are obtained through the ring-splitting polymerization of lactones in the presence of sorbitol. The polymerizates inter alia show improved resistance against heat and solvents and miscibility with other polymerizates. Derwent Abstract 86/106500 of J 60238317 describes alkyd resins for coating wood, metal, plastic materials and the like, with these containing a graft polymerizate which can be obtained by splitting the ring of cyclic esters in the presence of hydroxy cellulose derivatives. The alkyd resins show inter alia improved hardness and weather resistance and are, for example, component parts of paints for metals and wood.